Environmental Science
How Emerging Contaminants Like Pharmaceuticals Bioaccumulate in Aquatic Food Chains
Quick fact
Diclofenac, a common anti-inflammatory drug, can bioaccumulate in fish up to 500 times the concentration found in the surrounding water, and levels can increase by up to 10 times at each step of the food chain.
Why this is interesting
You take a painkiller and flush it down the drain—where does it go? And how could a drop of medicine in a lake end up concentrated in the fish on your plate?
Read the full explanation
Understanding How Emerging Contaminants Like Pharmaceuticals Bioaccumulate in Aquatic Food Chains
Imagine a lake. Pharmaceuticals from human use enter the water through sewage, even after treatment, since many are not completely removed. These chemicals are often 'lipophilic'—they dissolve in fats—so when tiny organisms like algae and zooplankton absorb them, they store them in their fatty tissues. When a small fish eats many zooplankton, it ingests the chemicals from all those tiny prey, and because its body doesn't easily break them down, they accumulate. Now a larger fish eats many smaller fish, concentrating the pharmaceuticals even further. Each step up the food chain—from plankton to fish to birds or humans—concentrates the drug, a process called biomagnification. This is why even tiny environmental concentrations can lead to biologically meaningful doses at the top of the food chain.
A deeper explanation
The underlying driver is the combination of lipophilicity and persistence. Lipophilic compounds readily pass through cell membranes and accumulate in fat, while their resistance to metabolism means they stay in the body. Bioaccumulation is the net result of uptake (through gills or ingestion) exceeding elimination (metabolism or excretion). Biomagnification is the consequence of each trophic level consuming a large mass of prey, so that between 1% and 10% of the accumulated load is retained and transferred upward. Pharmaceuticals vary in their persistence: some, like diclofenac, are moderately persistent, while others like antibiotics may be degraded, but their continuous, high-volume introduction into waterways effectively keeps environmental concentrations high. Moreover, many pharmaceuticals are designed to be biologically active at low doses, so even modest concentrations can affect non-target organisms. For example, the anti-inflammatory diclofenac causes renal failure in fish, and the painkiller ibuprofen has been shown to disrupt fish reproduction. This matters because these contaminants can disrupt entire food webs, and they often act in mixtures, where effects can compound. Emerging contaminants thus challenge the traditional focus on legacy POPs because they are not always as persistent, but their continuous release and biological activity make them similarly dangerous.